I've got a 03 silverado with the 5.3 liter in it. I've used since 7000 miles on the clock M1 5W-30 around 5-6000 mile intervals. Just passed 40k miles. I've been reading a lot on this site and am considering trying the M1 Euro car 0W-40 or the M1 T.S. 5W-40 oil. What do you guys think? I'll be doing my first UOA on the current batch of 5W-30 and hopefully I'll be able to do UOA's on the others. I'm thinking the Truck and Suv formula for the summer and the euro formula for winter. I work the truck pretty hard durning the winter and cold starts of -35 are very possible. So far I've only noticed piston slap or clatter once or twice in extreme conditions. It's actually been pretty good for me so far. Should I switch to one of these two oils, or stick with what seems to be working good?